1. Field of the Invention
This invention relates to an apparatus for measuring the mass rate of flow of fluids.
2. Description of the Related Art
Many apparatus already exist for measuring mass flow on the basis of different principles: densimetric correction, gyroscopic correction, Coriolis effect, etc. One of these apparatus which is currently used comprises two rotors connected to each other through a resilient member such as a spring. Such an apparatus is described for example in U.S. Pat. No. 2,943,487. The torsion angle of the two rotors, i.e. the phase shift between the first rotor and the second rotor, is proportional to the kinetic energy of the fluid, i.e. to the product of the density d of the fluid multiplied by the square of the rate of flow v of the fluid. In addition, the rotary speed of the rotor is proportional to the rate of flow v of the fluid. It is noted that by taking the ratio between the phase-shift angle of the two rotors, proportional to dv.sup.2, and the rotary speed v of the rotor, one obtains a quantity which is proportional to the product of the density of the fluid d multiplied by the speed v of the flowing fluid, i.e. proportional to the mass flow d.multidot.v of the fluid. In practice, the time interval corresponding to the phase-shift angle of the two rotors is measured. This type of flowmeter has numerous embodiments, one of which is described for example in U.S. Pat. No. 3,604,265.
In another type of mass flowmeter, use is made of two rotors mounted coaxially in the conduit traversed by the fluid. The two rotors can rotate independently of each other. The first rotor is used to give the fluid a rotational movement with respect to the conduit axis. The rotating fluid then creates a torque on the second rotor. This torque, which is proportional to the mass flow, is measured. An embodiment of a flowmeter of this type is described in U.S. Pat. No. 3,555,900.
It is moreover known that measuring the flow rate of a fluid by means of a turbine-type apparatus does not provide sufficient accuracy unless the flow of fluid within the meter takes place under turbulent conditions. Flow in the conduit is initially laminar for low speeds and then becomes turbulent as of a speed defined by the Reynolds formula. In order to broaden the measurement range with turbine-type flowmeters, an effort was made to modify the type of flow at low speed, i.e. to make it turbulent even for low flow rates. For this purpose, French Pat. No. 1 286 833 proposed a turbine-type flowmeter having either several propellers whose blades have different inclinations from one propeller to another, or a single propeller whose blades have at least two different inclinations, so as to communicate to the fluid the nonrectilinear trajectories which favor the establishment of turbulent flow.
Mass flowmeters with two turbines have the drawback of including many moving parts. There is in fact a risk of jamming of certain parts due to wear and to corrosion by the fluid. In addition, the inertia of the system increases as the number of moving parts increases. The result is a greater difficulty in measuring pulsed flows.